Stockholders' Equity - Summary of Stock Option Activity under the Company's Equity-Based Plans (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning Balance	6,281,148
Number of Shares, Granted	2,748,500
Number of Shares, Exercised	(1,712,278)
Number of Shares, Forfeited	(417,980)
Number of Shares, Expired	(6,580)
Number of Shares, Ending Balance	6,892,810	6,281,148
Number of Shares, Exercisable, Ending Balance	1,735,148
Number of Shares, Vested and expected to vest, Ending Balance	6,600,369
Weighted-Average Exercise Price, Beginning Balance	$ 1.74
Weighted-Average Exercise Price, Granted	$ 13.02
Weighted-Average Exercise Price, Exercised	$ 1.28
Weighted-Average Exercise Price, Forfeited	$ 5.33
Weighted-Average Exercise Price, Expired	$ 0.50
Weighted-Average Exercise Price, Ending Balance	$ 6.13	$ 1.74
Weighted-Average Exercise Price, Exercisable, Ending Balance	$ 1.20
Weighted-Average Exercise Price, Vested and expected to vest, Ending Balance	$ 6.01
Weighted-Average Remaining Contractual Term (Years)	8 years 2 months 19 days	8 years 6 months 18 days
Weighted-Average Remaining Contractual Term (Years), Exercisable	7 years 1 month 2 days
Weighted-Average Remaining Contractual Term (Years), Vested and Expected to vest	8 years 2 months 9 days
Aggregate Intrinsic Value, Beginning Balance	$ 53,373
Aggregate Intrinsic Value, Ending Balance	173,338	53,373
Aggregate Intrinsic Value, Exercisable, Ending Balance	52,195
Aggregate Intrinsic Value, Vested and expected to Vest, Ending Balance	$ 166,806